Lumbar supports exist in various forms to support the lumbar region of the human spine. Many of these prior art designs include a support which extends outwardly or curves outwardly to produce support against an appropriate position of the back. While prior art designs for adjusting the horizontal position of a lumbar support in this manner are known, these mechanisms typically include a large number of parts and are difficult, time-consuming, and costly to manufacture.
In addition, while a number of designs do provide for the horizontal adjustment of a back support, many of these do not include means for adjusting the vertical position of the support, thus reducing the available range of support positions and the potential for users of different shapes and sizes to use the seat. While prior art designs for adjusting both the horizontal and vertical positions of a lumbar support are known, these mechanisms are again complex and expensive to manufacture. More importantly it is generally desirable to minimize the thickness and size of the seat back, particularly with respect to any horizontal adjustment mechanism; something which complex and intricate lumbar support mechanisms do not generally permit.
For instance, U.S. Pat. No. 4,295,681 to Gregory shows a lumbar support device having two control means; one for adjusting the outward movement of the lumbar support and the other for adjusting the height of the lumbar support. Gregory uses a relatively large and complex mechanism consisting of a pair of link members and trunnions located on a threaded adjustment nut, one of which is on a shaft having a right hand thread, and the other is on a shaft having a left hand thread.
In Barley, U.S. Pat. No. 4,313,637, the lumbar support mechanism is positioned between spaced pairs of support arms. The respective arms of each pair are connected to define levers which adjust the amount of lumbar support which is provided.
Zacharkow, in U.S. Pat. No. 4,981,325, discloses a chair back having an upper back support member and a lower back support member. The lumbar support mechanism uses arms that extend from a threaded rod and are pivotally connected to the cushion which provides the lumbar support. The means for controlling the tilt of the lumbar support cushion is provided between the end of the arm and the cushion.
Sessini, U.S. Pat. Nos. 5,335,965 and 5,567,011, discloses a horizontally and vertically adjustable lumbar support device which utilizes a curved elastic plate and two vertically disposed threaded rods. The distal end of each rod in non-rotatably connected to one end of the curved elastic plate while the inner end of each rod is threadedly received in cylindrical scroll. The control is positioned an the side of the seat back and is connected to the lumbar support by multiple linkages. The support is adjusted vertically on a pair of vertical guides by means of control mechanism which includes a cord.
All of these support mechanisms require relatively large and complex mechanisms to enable adjustment of the amount of lumbar support which is provided by the device. Simplicity, reliability, and durability of design are also especially important since the lumbar adjustment mechanisms are generally located, for the most part, inside the upholstered seat back of the chair, and repairs are often difficult if not impossible to make.
Sheldon, U.S. Pat. No. 4,730,871, discloses a device which includes a vertical track and a guide made of spring steel which is mounted to be movable up and down in the track. The guide has a central portion spaced from the track to which the lumbar support member is attached. A screw member extends through the track to the lumbar support member. Rotation of the screw member allows the lumbar support member to be loosened to move vertically in the track and also causes the lumbar support member to be drawn rearwardly or pushed forwardly. While Sheldon discloses a simpler device, one problem with this mechanism is that a single control is used to adjust the vertical and horizontal adjustment of the lumbar support. Thus, the setting of the position and the amount of lumbar support are not independent. For example, when adjusting the height of the lumbar support, the amount of lumbar support may be affected.